(Configuration of Plasma Display Panel)
An AC surface discharge type panel that is typical as a plasma display panel (hereinafter abbreviated as a “panel”) includes a number of discharge cells between a front plate and a back plate arranged so as to face each other.
The front plate is constituted by a front glass substrate, a plurality of display electrodes, a dielectric layer and a protective layer. Each display electrode is composed of a pair of scan electrode and sustain electrode. The plurality of display electrodes are formed in parallel with one another on the front glass substrate, and the dielectric layer and the protective layer are formed so as to cover the display electrodes.
The back plate is constituted by a back glass substrate, a plurality of data electrodes, a dielectric layer, a plurality of barrier ribs and phosphor layers. The plurality of data electrodes are formed in parallel with one another on the back glass substrate, and the dielectric layer is formed so as to cover the data electrodes. The plurality of barrier ribs are formed in parallel with the data electrodes, respectively, on the dielectric layer, and the phosphor layers of R (red), G (green) and B (blue) are formed on a surface of the dielectric layer and side surfaces of the barrier ribs.
The front plate and the back plate are arranged to face each other such that the display electrodes intersect with the data electrodes in three dimensions, and then sealed. An inside discharge space is filled with a discharge gas. The discharge cells are formed at respective portions at which the display electrodes and the data electrodes face one another.
In the panel having such a configuration, a gas discharge generates ultraviolet rays, which cause phosphors of R, G and B to be excited and to emit light in each of the discharge cells. Accordingly, color display is performed.
A sub-field method is employed as a method of driving the panel. In the sub-field method, one field period is divided into a plurality of sub-fields, and the discharge cells are caused to emit light or not in the respective sub-fields, so that a gray scale display is performed. Each of the sub-fields has a setup period, a write period and a sustain period.
(Driving Method 1 of Conventional Panel)
In the setup period, a weak discharge (setup discharge) is performed to form wall charges required for a subsequent write operation in each discharge cell. In addition, the setup period has a function of generating priming for reducing a discharge time lag to stably generate a write discharge. Here, the priming means an excited particle that serves as an initiating agent for the discharge.
In the write period, scan pulses are applied to the scan electrodes in sequence while write pulses corresponding to image signals to be displayed are applied to the data electrodes. This selectively generates the write discharges between the scan electrodes and the data electrodes, causing the wall charges to be selectively formed.
In the subsequent sustain period, the sustain pulses are applied between the scan electrodes and the sustain electrodes a predetermined number of times corresponding to luminances to be displayed. Accordingly, discharges are selectively induced in the discharge cells in which the wall charges have been formed by the write discharges, causing the discharge cells to emit light.
Here, respective voltages applied to the scan electrodes, the sustain electrodes and the data electrodes are adjusted in order to generate the weak discharges in the discharge cells in the foregoing setup period.
Specifically, a ramp voltage gradually rising is applied to the scan electrodes while the voltage of the data electrodes is held at a ground potential (a reference voltage) in the first half of the setup period (hereinafter referred to as a rise period). This generates the weak discharges between the scan electrodes and the data electrodes and between the sustain electrodes and the data electrodes in the rise period.
Moreover, a ramp voltage gradually dropping is applied to the scan electrodes while the voltage of the data electrodes is held at the ground potential in the second half of the setup period (hereinafter referred to as a drop period). This generates the weak discharges between the scan electrodes and the data electrodes and between the sustain electrodes and the data electrodes in the drop period.
As described above, Patent Document 1, for example, discloses the method of driving the panel in which the ramp voltage or the voltage gradually rising or dropping is applied to the scan electrodes during the setup period. Thus, the wall charges stored on the scan electrodes and sustain electrodes are erased, and the wall charges required for the write operation are stored on each of the scan electrodes, the sustain electrodes and the data electrodes.
In practice, however, strong discharges may be generated between the scan electrodes and the data electrodes in the rise period. In this case, the strong discharges are generated between the scan electrodes and the sustain electrodes to generate a large amount of wall charges and a large amount of priming in the discharge cells, resulting in a higher possibility of the strong discharges to be generated also in the drop period.
The generation of the strong discharges in the setup period erases the wall charges stored on the scan electrodes, the sustain electrodes and the data electrodes. Thus, an appropriate amount of wall charges required for the write discharges cannot be formed on each electrode.
Therefore, Patent Document 2 discloses a method of driving the panel that prevents the generation of the strong discharges in the setup period.
(Driving Method 2 of Conventional Panel)
FIG. 24 shows examples of driving voltage waveforms (hereinafter referred to as driving waveforms) of the panel employing a method of driving the panel of Patent Document 2. FIG. 24 shows the waveforms of driving voltages applied to the scan electrodes, the sustain electrodes and the data electrodes, respectively, in the sustain period, the setup period and the write period.
As shown in FIG. 24, the data electrodes are held at a voltage Vd that is higher than the ground potential in the rise period of the setup period.
In this case, a voltage between the scan electrodes and the data electrodes is smaller than that when the data electrodes are held at the ground potential. Accordingly, a voltage between the scan electrodes and the sustain electrodes exceeds a discharge start voltage before the voltage between the scan electrodes and the data electrodes exceeds the discharge start voltage.
As described above, the weak discharges are induced between the scan electrodes and the sustain electrodes at an earlier timing, thereby generating the priming in the rise period. After that, the weak discharges are induced between the scan electrodes and the data electrodes, so that the wall charges required for the write operation are formed on each of the scan electrodes, the sustain electrodes and the data electrodes.
For example, the negative wall charges are stored on the scan electrodes and the positive wall charges are stored on the data electrodes when the write period shown in FIG. 24 is started. This results in stable write discharges in the write period.
[Patent Document 1] JP 2003-15599 A
[Patent Document 2] JP 2006-18298 A